A conventional traction elevator typically comprises a car, a counterweight and traction means such as a rope, cable or belt interconnecting the car and the counterweight. The traction means passes around and engages with a traction sheave which is driven by a motor. The motor and the traction sheave rotate concurrently to drive the traction means, and thereby the interconnected car and counterweight, along an elevator hoistway. At least one brake is employed in association with the motor or the traction sheave to stop the elevator and to keep the elevator stationary within the hoistway. A controller supervises movement of the elevator in response to travel requests or calls input by passengers.
Generally, the brakes must satisfy strict regulations. For example, both the ASME A17.1-2000 code in the United States and European Standard EN 81-1:1998 state that the elevator brake must be capable of stopping the motor when the elevator car is travelling downward at rated speed and with the rated load plus 25%.
Furthermore, the elevator brake is typically installed in two sets so that if one of the brake sets is in anyway faulty, the other brake set still develops sufficient braking force to slow down an elevator car travelling at rated speed and with rated load.
Given the vital nature of the elevator brake, it can be important that it is tested periodically. WO-A2-2005/066057 describes a method for testing the condition of the brakes of an elevator. In an initial calibration step of the method, a test weight is applied to the drive machine of the elevator and a first torque required for driving the elevator car in the upward direction is measured. Subsequently, the test weight is removed and at least one of the brakes or brake sets of the elevator is closed. Next, the empty elevator car is driven in the upward direction with the force of the aforesaid first torque and a check is carried out to detect movement of the elevator car. If movement of the elevator car is detected, then the aforesaid at least one brake of the elevator is regarded as defective.
A similar test method is disclosed in WO-A2-2007/094777 except that instead of using a test weight for calibration, a test torque is somehow preset and stored in an undisclosed way within the controller. With at least one of the brakes applied, the preset test torque is applied by the motor to move the empty elevator car. Any movement of the car is determined by either a position encoder or a hoistway limit switch. As before, if movement of the elevator car is observed, then the aforesaid at least one brake of the elevator is regarded as defective.
In both of the above test procedures, if a faulty brake has been detected the elevator is disabled and is no longer able to fulfill passengers travel requests. The elevator remains out of commission until the effected brake is replaced.